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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > PFC (Power Factor Correction)

Texas Instruments UCC3858N

Name: UCC3858N
Brand: Texas Instruments
SKU: UCC3858N
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: UCC3858N

Manufacturer:: Texas Instruments

Category:: PFC (Power Factor Correction)

Package:: 16-DIP (0.300", 7.62mm)

Datasheet:: UCC3858N.pdf

Description:: POWER FACTOR CONTROLLER

Quantity:: RFQ Add To RFQ list

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Product details

Overview

UCC3858N from Texas Instruments is a high-efficiency, active power factor correction (PFC) controller IC designed for boost preregulators in low-to-medium-power AC/DC systems. It implements average current mode control to shape line current waveform to match line voltage, achieving near-unity power factor. Key confirmed parameters include 12V–18V VDD operating range, 100 µA startup supply current, leading-edge PWM modulation, programmable frequency foldback down to 25 kHz, and integrated RMS voltage detection via CRMS pin.

For engineers reviewing the UCC3858N datasheet, UCC3858N pinout, UCC3858N application, or UCC3858N equivalent, this page delivers verified technical context on light-load efficiency optimization, synchronization with downstream DC-DC converters, peak current limiting at MOUT, transconductance voltage error amplifier behavior, and design-critical timing relationships between FBL, FBM, CT, and RT pins.

Technical Context

The UCC3858N uses average current mode control with a transconductance voltage error amplifier (400–1000 µS gain) and a wide-bandwidth current amplifier to enforce sinusoidal input current. Its oscillator supports both free-running (100 kHz typical) and synchronized operation via SYNC pin, with leading-edge PWM output to reduce bulk capacitor ripple current when paired with trailing-edge downstream converters.

Frequency foldback is implemented by linearly scaling oscillator charging current based on VAO–FBL differential voltage, reducing switching frequency under light load while maintaining stability. An instantaneous reset path via FBM pin allows rapid exit from foldback mode using external circuitry tied to the downstream converter's error amplifier.

Key Specifications

Parameter	Value and Actual Design Meaning
VDD Range	12 V to 18 V - defines minimum bootstrap supply voltage and maximum safe bias rail; UVLO turn-on at 12–15.5 V ensures reliable offline startup.
Startup Current	100 µA typical - enables high-value trickle-charge resistors, minimizing standby losses in auxiliary supplies.
Oscillator Frequency	80–120 kHz (total variation) - set by RT/CT network; foldback reduces minimum to 25–30 kHz to cut core and switching losses at light load.
Reference Voltage	7.5 V ±2.5% over temperature - used for feedback divider biasing and internal overvoltage protection threshold reference.
Peak Current Limit Threshold	350–550 mV at MOUT - sets cycle-by-cycle current limit without external comparator; hysteresis of 100–200 mV prevents oscillation.
RMS Detection Accuracy	No external 2-pole filter required - internal peak detector and CRMS capacitor integration eliminate second-harmonic distortion in VRMS signal, improving THD <3%.
Gate Drive Output	7 Ω pull-up / 3.5 Ω pull-down - supports fast MOSFET switching (20–25 ns rise/fall) with external series resistor ≥5 Ω for ringing suppression.

Pinout & Package

UCC3858N is housed in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and standard through-hole mounting. Thermal resistance θ_JA is 65°C/W (typical), requiring adequate PCB copper area for >1 W dissipation.

Pin/Terminal	Circuit Role	Design Meaning
1 (CA–)	Current amplifier inverting input	Accepts sensed current signal from R_SENSE; operates down to GND for zero-duty-cycle capability.
2 (CAO)	Current amplifier output	Drives PWM comparator; rail-to-rail swing enables full duty-cycle control and precise current regulation.
3 (CRMS)	RMS voltage integration node	Connects to external capacitor (75–90 nF); internal IAC mirroring charges it each half-cycle for accurate line-voltage feedforward.
4 (CT)	Oscillator timing capacitor	Timing node for ramp generation; discharge current set by RT; determines base switching frequency per f = 0.814/(R_TC_T).
5 (FBL)	Frequency foldback level select	Sets VAO threshold for foldback initiation; pulling below 0.5 V disables IC entirely.
6 (FBM)	Minimum frequency reference	Sets lowest foldback frequency via R_FBM; pulled low (<1.5 V) forces immediate return to nominal frequency.
7 (GND)	Power and signal reference	Return path for CT discharge, gate drive sink, and all analog circuits; requires short, low-inductance trace to bypass caps.
8 (IAC)	AC line current input	Current-mode multiplier input; accepts 20–100 µA; needs ≤330 pF bypass for noise immunity.
9 (MOUT)	Multiplier output / current amp non-inverting input	High-impedance node combining multiplier current and sense voltage; used for peak current limiting at –0.5 V.
10 (OUT)	Gate driver output	Totem-pole DMOS stage driving external MOSFET gate; rated for 500 mA pulsed, requires series resistor ≥5 Ω.
11 (RT)	Oscillator timing resistor	Sets oscillator discharge current (I_DIS = 3/R_T); works with CT to define free-running frequency and foldback slope.
12 (SYNC)	Oscillator synchronization input	Accepts rising-edge sync pulse from downstream converter; resets CT ramp to align PFC and DC-DC switching edges.
13 (VA–)	Voltage amplifier inverting input	Connected to output voltage divider; triggers overvoltage shutdown if >3.15 V; sets regulation point for V_OUT.
14 (VAO)	Voltage amplifier output	Transconductance amplifier output (0.3–6.3 V swing); controls PWM duty and initiates foldback when falling below FBL.
15 (VREF)	7.5 V precision reference	Supplies bias to external circuitry (≤10 mA); disabled when VDD < UVLO; requires 0.1 µF ceramic bypass to GND.
16 (VDD)	Positive supply input	Power pin accepting 12–18 V; must be bypassed with ≥0.1 µF ceramic cap directly to GND to handle gate-drive current spikes.

Key Features

Feature	Design Value
Programmable frequency foldback	Reduces switching frequency linearly as load drops, cutting core loss and diode conduction loss without compromising regulation.
Leading-edge PWM modulation	Enables optimal ripple cancellation when synchronized with trailing-edge downstream converters, lowering bulk capacitor RMS current by ~50%.
Integrated RMS voltage detection	Eliminates external 2-pole filter; improves line transient response 6× and removes second-harmonic distortion in input current waveform.
Cycle-by-cycle peak current limiting	Uses MOUT node voltage (–0.5 V threshold) for fast, accurate overcurrent protection without added sensing components.
Low quiescent current architecture	100 µA startup and 2–5 mA operating current enable efficient auxiliary supply design and extended hold-up time at light loads.

Applications

Server Power Supplies	LED Driver Front-Ends
Use Scenario: 300–500 W AC/DC front-end in 1U rack servers requiring >95% efficiency at 20% load and EN61000-3-2 Class C compliance. IC Role / Device Role / Timing Role: UCC3858N serves as the active PFC controller, regulating boost stage to deliver stable 385 V DC bus while enforcing sinusoidal input current synchronized to line voltage. Use Value: Frequency foldback maintains >92% efficiency at 10% load; leading-edge PWM + SYNC reduces bulk capacitor stress and extends lifetime by lowering ΔT.	Use Scenario: 150 W constant-current LED driver for commercial lighting with universal 90–264 VAC input and tight THD limits. IC Role / Device Role / Timing Role: UCC3858N configures the boost PFC stage preceding a flyback or LLC controller, delivering regulated high-voltage DC bus with <5% THD. Use Value: Integrated RMS detection eliminates filter drift errors; CRMS-based feedforward ensures consistent power factor >0.98 across full input range without recalibration.
Industrial Motor Drives	Medical AC/DC Adapters
Use Scenario: 200 W variable-speed drive for HVAC blowers where EMI reduction and light-load efficiency are critical for fan speed modulation. IC Role / Device Role / Timing Role: UCC3858N controls interleaved or single-phase boost PFC to supply clean DC link for inverter stage, synchronized to downstream PWM via SYNC pin. Use Value: Synchronization cuts conducted EMI peaks by 10–15 dB; foldback minimizes audible noise at low speeds by avoiding audio-frequency switching.	Use Scenario: 65 W medical-grade AC/DC adapter certified to IEC 60601-1, requiring low leakage current, high reliability, and no derating below 25°C ambient. IC Role / Device Role / Timing Role: UCC3858N implements isolated PFC stage with undervoltage lockout (13.5 V turn-on) and overvoltage shutdown (3.15 V at VA–) for fail-safe operation. Use Value: 7.5 V VREF powers optocoupler bias and feedback circuitry; low 100 µA startup current enables compact, transformerless auxiliary supply design.

Server Power Supplies

LED Driver Front-Ends

Use Scenario: 300–500 W AC/DC front-end in 1U rack servers requiring >95% efficiency at 20% load and EN61000-3-2 Class C compliance.

IC Role / Device Role / Timing Role: UCC3858N serves as the active PFC controller, regulating boost stage to deliver stable 385 V DC bus while enforcing sinusoidal input current synchronized to line voltage.

Use Value: Frequency foldback maintains >92% efficiency at 10% load; leading-edge PWM + SYNC reduces bulk capacitor stress and extends lifetime by lowering ΔT.

Use Scenario: 150 W constant-current LED driver for commercial lighting with universal 90–264 VAC input and tight THD limits.

IC Role / Device Role / Timing Role: UCC3858N configures the boost PFC stage preceding a flyback or LLC controller, delivering regulated high-voltage DC bus with <5% THD.

Use Value: Integrated RMS detection eliminates filter drift errors; CRMS-based feedforward ensures consistent power factor >0.98 across full input range without recalibration.

Industrial Motor Drives

Medical AC/DC Adapters

Use Scenario: 200 W variable-speed drive for HVAC blowers where EMI reduction and light-load efficiency are critical for fan speed modulation.

IC Role / Device Role / Timing Role: UCC3858N controls interleaved or single-phase boost PFC to supply clean DC link for inverter stage, synchronized to downstream PWM via SYNC pin.

Use Value: Synchronization cuts conducted EMI peaks by 10–15 dB; foldback minimizes audible noise at low speeds by avoiding audio-frequency switching.

Use Scenario: 65 W medical-grade AC/DC adapter certified to IEC 60601-1, requiring low leakage current, high reliability, and no derating below 25°C ambient.

IC Role / Device Role / Timing Role: UCC3858N implements isolated PFC stage with undervoltage lockout (13.5 V turn-on) and overvoltage shutdown (3.15 V at VA–) for fail-safe operation.

Use Value: 7.5 V VREF powers optocoupler bias and feedback circuitry; low 100 µA startup current enables compact, transformerless auxiliary supply design.

Equivalent & Alternatives

The following parts are listed as comparable options for similar active PFC controller applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
UC3854BDW	Fixed 100 kHz oscillator; no frequency foldback; no integrated RMS detection; requires external 2-pole VRMS filter.	Lacks light-load efficiency optimization; higher THD at low line; less robust line transient response.	Choose UC3854BDW only if legacy design reuse is required and foldback/RMS features are unnecessary.
UCC28070DR	Continuous conduction mode (CCM) PFC controller with digital current sense; 65 kHz fixed frequency; no SYNC pin; no CRMS-based feedforward.	Designed for higher-power (>300 W) applications; lacks analog RMS integration and leading-edge PWM flexibility.	Prefer UCC28070DR for new high-power designs needing digital control headroom, but not for UCC3858N's light-load or synchronization use cases.

Compared with UC3854BDW and UCC28070DR, the UCC3858N uniquely combines analog RMS feedforward, programmable frequency foldback, and SYNC-enabled leading-edge PWM-making it the only option among the three that simultaneously optimizes light-load efficiency, THD performance, and ripple-current reduction in sub-300 W PFC stages.

Availability

UCC3858N is available at Aetrix Electronics and suitable for server power supplies, LED driver front-ends, industrial motor drives, medical AC/DC adapters, and telecom rectifiers requiring stable component supply despite its obsolete status.

Supply support for UCC3858N includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The UCC3858N belongs to TI's legacy Unitrode PFC controller product line, engineered specifically for cost-sensitive, high-efficiency AC/DC front-ends where light-load operation, THD compliance, and board-level integration are primary design constraints.

FAQ

What is the operating temperature range for the UCC3858N?

The UCC3858N is specified for operation from 0°C to +70°C ambient temperature. This range is explicitly defined in the Electrical Characteristics table and applies to all key parameters including oscillator accuracy, reference voltage, and amplifier gains. The device's junction temperature rating extends to +150°C, but sustained operation above +70°C ambient requires careful thermal design due to its PDIP package's 65°C/W θ_JA. Derating curves are not provided in the datasheet, so thermal margin must be validated per application.

How does the UCC3858N implement frequency foldback, and what pins control it?

The UCC3858N implements frequency foldback by reducing the CT ramp charging current as the VAO voltage falls below the level set at the FBL pin. The difference between VAO and FBL regulates a subtractive current (ICsub) that lowers effective charge current into CT. Minimum frequency is set by resistor R_FBM between FBM and VREF; pulling FBM below 1.5 V forces immediate exit from foldback. Thus, FBL and FBM are the dedicated control pins for initiating and overriding foldback in the UCC3858N.

Can the UCC3858N be synchronized to an external clock, and how is it configured?

Yes, the UCC3858N supports synchronization via its SYNC pin. A rising-edge pulse applied to SYNC resets the CT ramp, aligning the UCC3858N's switching edge with the downstream converter's clock. For reliable operation, the SYNC signal must be clean, fast-rising (<100 ns), and referenced to UCC3858N's GND. The free-running frequency must be set lower than the sync frequency using RT and CT values. This configuration is confirmed in Figure 3a and Application Note UDG-97120-1 for the UCC3858N.

What is the purpose of the CRMS pin on the UCC3858N, and what capacitor value is recommended?

The CRMS pin on the UCC3858N connects to an external capacitor that integrates mirrored IAC current over each AC half-cycle to generate an accurate RMS voltage representation. This eliminates the need for an external 2-pole filter and improves line transient response. For 50 Hz line, a 90 nF capacitor is recommended; for 60 Hz, 75 nF is optimal. These values ensure VCRMS reaches ~1 V at low line (80 VAC) and ~3.5 V at high line (265 VAC), as specified in the UCC3858N application section.

Does the UCC3858N provide overvoltage protection, and how is it triggered?

Yes, the UCC3858N provides internal overvoltage protection. It monitors the voltage at the VA– pin - which is connected to the output voltage divider - and terminates PWM output if VA– exceeds 3.15 V. This corresponds to a typical output overvoltage threshold of ~400 V for a standard 385 V DC bus with common resistor ratios. The protection is hardwired and does not require external components, making it a reliable fail-safe feature in the UCC3858N.

UCC3858N Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: -

Package/Case:: 16-DIP (0.300", 7.62mm)

Packaging:: Bulk

Product Status:: Active

Mode:: Average Current

Frequency - Switching:: 100kHz

Current - Startup:: -

Voltage - Supply:: 12V ~ 18V

Operating Temperature:: 0°C ~ 70°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 16-PDIP

UCC3858N FAQ

1.How can I place an order for UCC3858N through Aetrix?

Please submit a Request for Quotation (RFQ) for UCC3858N on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for UCC3858N reliable?

The price and inventory of UCC3858N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UCC3858N is usually 5 days.

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Once your UCC3858N order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for UCC3858N?

For technical support, including UCC3858N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UCC3858N requirements.

6.How does Aetrix verify that UCC3858N is sourced from the original manufacturer or authorized distributors?

All UCC3858N products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that UCC3858N meets industry standards.

7.What is the process for return or replacement of UCC3858N?

All UCC3858N units undergo pre-shipment inspection (PSI). If there is an issue with UCC3858N, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The UCC3858N part is unused and in its original packaging.

Return procedure for UCC3858N:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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